This is generally known as the ApoE4 allele of ApoE and is associated with increased risk of Alzheimer's. 20-25% of individuals are heterozygous for this variant, and 1-2% are homozygous. Data from Khachaturian et al. suggests an average 7% of all individuals developed Alzheimer's by the age of 80; when this is split by ApoE4 status: 10% of ApoE4 heterozygotes (3% increased attributable risk), 40% of ApoE4 homozygotes (33% increased attributable risk), and 5% of non-carriers (2% decreased attributable risk). Notably, their model suggests 70-75% of people would eventually develop Alzheimer's by the age of 100 regardless of ApoE4 genotype (and 25-30% are resistant, regardless of genotype), but that ApoE4 variants shift the disease onset to occur significantly earlier (4 years earlier for heterozygous carriers, 13 years for homozygotes).

Reported to cause arrhythmogenic right ventricular cardiomyopathy when compound heterozygous with G1885E, although this finding is weakened after correcting for multiple hypotheses and it is unclear what penetrance such a genotype might have, if it is causal.

Known as the "Marburg I" polymorphism, this variant is associated with increased risk of coronary heart disease (CHD) in individuals with elevated cholesterol, triglyceride, and fibrinogen levels (5-fold risk of a CHD event, compared to 2-fold risk increase in people with the same risk factors but do not have this variant). In individuals without these elevated levels, however, carriers of the variant do not appear to have any increased risk of CHD.

This common variant (HapMap allele frequency of 31.3%) in a protein involved in folate (B9) and cobalamin (B12) metabolism and is often reported as "MTRR I22M" (an alternative transcript position). Mothers homozygous for this variant are associated with having around a increased chance of a child with Down syndrome (risk of 0.4%, average risk in population is 0.25%). Notably, age plays a far larger role in the rate of Down syndrome (risk is 4.5% for a mother 45-years-of-age), and it is unknown how this variant may combine with the effect of age. There are conflicting reports associating this variant with incidence of neural tube defects, possibly when combined with MTHFR A222V.

This variant is associated with mannose binding protein deficiency which leads to impaired complement system immune response to mannose-rich pathogens. Patients homozygous for this allele or compound heterozygous are likely to have increased susceptibility to infection, but Hellemann et al. report heterosis for intensive care outcomes in heterozygous subjects. The wild-type version of this gene is known as variant allele A, while this is called variant allele B. See R52C (variant D) and G57E (variant C).

Causes Adenosine Deaminase Deficiency in a recessive manner. Most of the time individuals do not report symptoms, but when symptoms do exist they to be post-exercise symptoms of muscle weakness, muscle pain, and getting tired more quickly.

This variant in a growth factor gene is associated with variation in TGFB1 levels; this has been associated with various pathogenic and some protective effects, including: more hepatic fibrosis progression in hep C patients, lower risk of cleft palate, anticorrelation with longevity, higher risk of myocardial infarction and lower risk of hypertension.

This is a common variant was first reported as a polymorphism. It has since had mixed associations with cancer: Storey et al. conclude a 7x *increased* risk of HPV cancer for homozygotes vs hets, but Jones et al. find a 1.98x *decreased* risk for colorectal cancer. This variant may have significant impact on particular cancers, but it is unclear what effect it has on the overall burden of cancer.

This nonsynonymous SNP is associated with Wolfram Syndrome (known as DIDMOAD), which is characterized by early-onset non-autoimmune diabetes mellitus, diabetes insipidus, optic atrophy, and deafness) and to adult Type Two Diabetes Mellitus. The WFS1 gene maps to chromosome 4p16.3. The variant has been shown to be statistically associated with type II diabetes in six UK studies and one study of Ashkenazi Jews (Sandhu, M., et al., Minton et al.).

There have been some hypotheses that this variant contributes to causing hereditary hemochromatosis, possibly as a compound heterozygote, but some others treat it as a polymorphism. Cys282Tyr is the classic causal variant and itself has very low penetrance. Mouse studies indicates this variant has a similar but weaker effect; if it has any effect at all its penetrance may be quite low and/or require modifier alleles.

This common variant may have a small pathogenic effect by contributing to cortisone reductase deficiency (a rare abnormality) when homozygous and combined with a serious pathogenic variant. The same authors have tested and ruled out a contribution to polycystic ovary syndrome (similar phenotype, more common disease).

This variant is associated with a slightly increased risk of tuberculosis. It is unclear whether it is itself causal, or in linkage disequilibrium with some other causal variant that has a stronger effect.

Alone, this variant is known as TPMT*3C -- but often, especially in Caucasians, it is found together with another nonsynonymous variant (A154T) to produce the TPMT*3A variant. Both variants are associated with loss of thiopurine methyltransferase (TPMT) activity, although *3C is milder than *3A. Inability to metabolize thiopurine drugs can lead to severe adverse reactions. Heterozygotes may be advised to take a reduced dosage due to reduced metabolism of the drug.

Usually this variant is found in combination Y240C, forming the TPMT*3A variant. When alone, this variant produces the *3B variant. Both variants are associated with loss of thiopurine methyltransferase (TPMT) activity. Inability to metabolize thiopurine drugs can lead to severe adverse reactions. Heterozygotes may be advised to take a reduced dosage due to reduced metabolism of the drug.

This variant is associated with some protective effects for prion disease -- individuals homozygous for this variant are less susceptible to Creutzfeldt-Jakob, and Papua New Guinea individuals heterozygotes at this site are less susceptible to kuru.

The reference genome variant for this allele has been associated with a slight increased risk of multiple sclerosis. Thus, this variant can be treated as a "protective" variant -- carriers of this variant are slightly less likely to have MS. Because the disease is rare and the effect of this variant is not very strong, the absolute decreased risk for carriers of this variant is less than .05% (less than 1 in 2000).

This variant is associated with decreased risk of type 2 diabetes. It is unclear whether this variant has additive effects, or acts in a dominant or recessive manner. Assuming diabetes has a lifetime risk of 36%, we estimate a decreased risk of around 1-2% per copy of this variant.

Probably benign. Other mutations in this gene are implicated in causing hereditary paraganglioma or pheochromocytoma syndromes, but this variant is also found in unaffected controls and is considered a nonpathogenic polymorphism by most authors that have reported it.

Other mutations in this gene are associated with Factor 5 deficiency. There is no literature implicating this variant, however, and it is fairly common in the population (3.8% in HapMap), and so it is currently labeled as benign.

Probably benign. One report linked this variant to high triglycerides, but a later paper found a nearby SNP with similar association and suggests that both findings are caused by linkage to an undiscovered causal variant.

This variant is associated with "taster" status of PTC, along with 49P and 262A. Due to linkage disequilibrium, the independent effects of positions 296 and 262 is unclear. The presence of 49P confers taster status in a dominant fashion, but in the absence of 49P, the presence of 262A/296V is still positively associated with tasting PTC.